1. Field of the Invention
Embodiments of the present invention generally relate to apparatus and methods for selectively producing and/or treating one or more hydrocarbon bearing subterranean formations. More particularly, embodiments of the present invention relate to apparatus and methods for completing a subterranean well in which multiple zones may be selectively treated and produced. More particularly still, embodiments of the present invention relate to apparatus and methods for perforating the one or more formation(s) and selectively establishing fluid communication between the one or more formations and a well bore.
2. Description of the Related Art
In the drilling of oil and gas wells, a wellbore is formed using a drill bit disposed at a lower end of a drill string that is urged downwardly into the earth. After drilling to a predetermined depth or when circumstances dictate, the drill string and bit are removed and the wellbore is lined with a string of casing. An annular area is thereby formed between the string of casing and the formation. A cementing operation is then conducted in order to fill the annular area with cement. The combination of cement and casing strengthens the wellbore and facilitates the isolation of certain areas or zones behind the casing including those containing hydrocarbons. The drilling operation is typically performed in stages and a number of casing or liner strings may be run into the wellbore until the wellbore is at the desired depth and location.
The casing and cement and an adjacent hydrocarbon bearing formation or formations are typically perforated using a series of explosive or “perforating” charges. Such a series of charges may be lowered into the well bore casing inside of an evacuated tube and such a charge containing tube is a type of what is generally known as a “perforating gun.” When detonated, the charges pierce or perforate the walls of the casing and penetrate any adjacent cement and the adjacent formation thereby allowing fluid communication between the interior of the casing and the formation. Production fluids may flow into the casing from the formation and treatment fluids may be pumped from the casing interior into the formation through the perforations made by the charges.
In many instances a single wellbore may traverse multiple hydrocarbon bearing formations that are otherwise isolated from one another within the Earth. It is frequently desirable to treat such hydrocarbon bearing formations with pressurized treatment fluids prior to producing those formations or at some other time during the useful life of a well. In order to ensure that a proper treatment is performed on a desired formation, that formation is typically isolated from other formations traversed by the wellbore. It may also be desirable to produce a given formation or formations in isolation from other formations common to the traversing wellbore. Examples of selective formation stimulation treatment and production techniques are described in U.S. Pat. No. 5,823,265 to Crow et. al., and that patent is incorporated herein, in its entirety, by reference.
To achieve sequential treatment of multiple formations in a new well, the casing adjacent a lowermost formation is perforated while the casing portions adjacent other formations common to the wellbore are left un-perforated. The perforated zone is then treated by pumping treatment fluid under pressure into that zone through the perforations. Following treatment, a downhole plug is set above the perforated zone to isolate that zone. The next sequential zone up the wellbore (“up hole”) is then perforated, treated and isolated with an above positioned plug. That process is repeated until all of the zones of interest have been treated. Subsequent production of hydrocarbons from these zones requires that the sequentially set plugs be removed from the well. Such removal requires that removal equipment be run into the well on a conveyance string which string may typically be wire line, coiled tubing or jointed pipe.
Formation isolation in an existing perforated well may be achieved by proper placement of straddle packer arrangements and/or plugs. While selective treatment can be achieved using such equipment, the process and equipment can be complicated and expensive.
In the above described treatment processes the perforation and plug setting or straddle packer setting steps each represent a separate excursion or “trip” into and out of the wellbore with the required equipment. Each trip takes additional time and adds complexity to the overall effort. Such factors can be exacerbated when operating in wellbores that are not vertical and specialized conveyance equipment is often required in “horizontal” wellbores.
Therefore, there is a need for improved methods and apparatus for selectively establishing fluid communication with one or more formations. Further, there is a need for improved systems that can perforate multiple zones selectively isolate the wellbore from the zones. Further still, there is a need for improved methods and apparatus capable of selectively establishing fluid communication between a wellbore and one or more zones traversed by that wellbore.